JPH0118595B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a multilayer printed wiring board used in electronic devices and the like.

Conventional structure and its problems In recent years, printed wiring boards with conductive paint on both sides are easy to manufacture, require little capital investment, and can be mass-produced. , remote controllers, radios, toys, and other devices. Additionally, multilayer printed wiring boards using conductive paint are increasing in order to realize higher density wiring.

Conventionally, the manufacturing method for this type of multilayer printed wiring board was to form a circuit by etching the copper foil of the copper-clad laminate on both sides, then create a through hole in the board, and inject conductive paint such as silver paint into the through hole. Apply the paint and
It is known that after making electrical connections on both sides of the board, an insulating resist is applied on the copper foil circuit, and a jumper circuit is formed on top of it with conductive paint so as to cross the copper foil circuit. For example, as shown in FIG. 1a, in an insulating substrate 2 on which copper foil circuits 1 are formed on both sides, through holes 3 are formed by drilling, as shown in FIG. 1b.

Next, as shown in FIG.
b makes the front and back conductive. Next, as shown in FIG. 1d, an insulating resist 6 is printed on the through holes 4b and the copper foil circuit 1, leaving necessary circuits such as the jumper connection portion 5. Next, as shown in FIG. 1e, a jumper 7 is formed with silver paint, and then an overcoat 8 is printed on the jumper 7, and the outer shape is processed to produce a multilayer printed wiring board.

However, in the above method, since the curing time of the through-hole 4b by the conductive paint is long and the temperature is high, the copper foil of the connection land portion 5 of the jumper 7 of the conductive paint is significantly discolored. Therefore, the copper foil must be cleaned before printing the conductive paint jumper 7. Furthermore, since the insulating resist 6 is thick, it is often difficult to clean the copper foil properly, resulting in disadvantages such as poor connection reliability and large variations in resistance values.

Furthermore, since the insulating resist 6 is printed many times, there is a large difference in level from the copper foil, and when the conductive paint jumper 7 is printed, the edge of the jumper at the connection part becomes thinner and may break. It was hoped that the shortcomings would be resolved.

OBJECTS OF THE INVENTION In view of the above drawbacks, the present invention provides a method for manufacturing a multilayer printed wiring board that is capable of forming a highly reliable conductive paint jumper.

Structure of the Invention In order to achieve this object, the method for manufacturing a multilayer printed wiring board of the present invention involves drilling holes in the thickness direction of an insulating substrate having conductive patterns formed on both sides, and applying conductive paint into the through holes. At the same time as filling by printing, the conductive paint is also printed on the copper foil land portion to which the conductive paint jumper is connected. According to this manufacturing method, since the conductive paint is on the copper foil at the connection land of the jumper, the copper foil is not exposed directly to a high temperature atmosphere when the conductive paint is cured, so there is no discoloration and the silver jumper is printed before printing. Further, the step difference in the insulating resist can be reduced by the thickness of the conductive paint, and the edge portion of the jumper can have a uniform thickness, improving the reliability of the printed wiring board. Moreover, since it is performed at the same time as filling the conductive paint, this method can be performed without increasing the number of man-hours.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIGS. 2a to 2f show a method for manufacturing a multilayer printed wiring board according to an embodiment of the present invention. In FIGS. 2a and 2b, forming the through holes 3 by drilling in the insulating substrate 2 on which the copper foil circuits 1 are formed on both sides is the same as in the conventional example shown in FIGS. 1a and 1b. In the figure, 1 is a copper foil circuit, 2 is an insulating base, and 3 is a through hole. Next, as shown in FIG. 2c, silver paint 4a is filled into the through hole 3 by printing, and at the same time, silver paint 4b is printed on the jumper connection part 5. These silver paints 4a and 4b were cured in a heat oven at 150°C for 1 hour, and the through holes 4
c to electrically connect the front and back sides, and at the same time ensure electrical connection at the jumper connection portion 5. Next, as shown in FIG. 2d, an insulating resist 6 is printed several times so that the thickness is 40 to 50 μm where it intersects with the copper foil circuit 1. Next, as shown in Fig. 2e, a jumper line 7 is printed with silver paint, and then an overcoat 8 is printed as shown in Fig. 2f, and the external shape and parts insertion holes are formed by press punching. etc.

According to the manufacturing method configured as described above, since the connection between the copper foil circuit 1 and the conductive paint jumper 7 at the jumper connection part is reliable, in the reliability test, the jumper 7 with a design resistance value of 5Ω was With the conventional method, the initial resistance value was an average value of 5.5Ω and a standard deviation of 1.0Ω, but with this manufacturing method, the initial resistance value was reduced to an average value of 5.2Ω and a standard deviation of 0.3Ω, with small variations. Also, humidity test (55℃, 95%RH, 1000
With the conventional method, the average rate of change in resistance over time is 40
% with a standard deviation of 35%, but according to this manufacturing method, the average resistance value was 30% and the standard deviation was 10%, and the stability of the resistance value was excellent. As described above, according to this embodiment, a highly reliable jumper circuit can be formed.

Note that although silver paint is used in this embodiment, other conductive paints may also be used.

Effects of the Invention As described above, the present invention forms a circuit by filling a conductive paint into a through hole and at the same time printing the conductive paint on a copper foil connecting land of a conductive paint jumper. The resistance value can be stabilized and its dispersion can be reduced, and the practical effect is great because it does not involve an increase in the number of man-hours.

[Brief explanation of drawings]

Figures 1a to 1f are cross-sectional views of each process for explaining a conventional method for manufacturing a multilayer printed wiring board;
Figures a to f are cross-sectional views of each process for explaining a method for manufacturing a multilayer printed wiring board in an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Copper foil circuit, 2... Insulating substrate, 3... Through hole, 4... Conductive paste, 4'... Conductive paint through hole, 5... Conductive jumper connection land, 6... Insulating resist, 7 ...Conductive jumper, 8...Overcoat.

Claims (1)

[Claims] 1 After drilling holes in the thickness direction of an insulating board with copper foil circuits formed on both sides, when filling the through holes with conductive paint by printing, a copper foil land is used to connect the jumper wire using the conductive paint. A method for manufacturing a multilayer printed wiring board, characterized in that the conductive paint is simultaneously printed on the part, the insulation resist is printed, the conductive paint and the jumper wire are printed, and an overcoat is formed thereon.